Cordon blue

In the past few weeks an 11-mile blue fence has sprung up around the 2012 Olympics site in east London. Is it a necessary security measure - or a reminder of how divisive the games are? Andy Beckett walks along it.

Silke Dettmers is an east London sculptor who makes spindly and ominous wooden miniatures of imaginary buildings. She also teaches art students about graphic design and the sly workings of modern branding and advertising. Yet recently she has developed another interest. It revolves around the colour blue. Not just any blue, but a vivid, electric cyan that dazzles the eye, that seemingly has little to do with any blue in the natural world. Since August she has been tracing the use of this colour across a great swath of east London, taking photographs of it, collecting scraps of blue wood, hoarding them in her studio. "I am absolutely determined," she says, "to make a sculpture out of this blue."

Yet for Dettmers, and for many other Londoners, this unashamedly chemical, attention-seeking hue is more than the basis of a notional art project; it is, in a sense, the colour of the future. Over the past few weeks, without much publicity, a great blue ring has been closing around several square miles of Hackney Wick and Stratford in the eastern flatlands of the capital. This painted fence, more than 10ft high and set in concrete footings, is the boundary and the most obvious manifestation so far of a new city-within-a-city, its perimeter stretching 11 miles: the 2012 Olympic park. The erection of this barrier, through which no visitor can pass now without official permission, follows the removal from the Olympic site of allotment holders and traveller families, of long-established artists' studios and local businesses. It is an even less delicate reminder that the Olympics and their accompanying schemes for urban regeneration, whether you favour them or not, are going to come to east London at a price.

According to the press office of the Olympic Delivery Authority (ODA), the fence is for "health and safety reasons, primarily ... With demolition work on the Olympic Park accelerating it is essential we install hoardings around the site to protect the safety of local residents and our workforce." But these days a barrier built across a city inescapably has other, less benign associations: the Israeli wall around the occupied territories, the fortifications around the green zone in Baghdad, the Berlin Wall, the "peace walls" in Belfast. Such comparisons may be disproportionate, even tasteless, yet the fact remains that the 2012 fence is intended to stand for almost half a decade, until the Olympic facilities are finished. Given the security needs of the Olympics themselves, a more formidable border is likely to replace it. Different Londons will develop on either side of this divide, and the consequences will be felt in the city for decades. These consequences may act as an inspiration to other cities, or as a warning.

On Monday this week I met Dettmers to explore the fence and its neighbourhood. It was a low and grey London morning. In the car on the way to Hackney Wick she told me that over the weekend she had been arrested. "I was standing on a bridge overlooking the Olympic development," she said, "getting the light to take a picture, and I had a little encounter with the police. They did a stop-and-search on me, on suspicion of being a terrorist. I told them who I was, and why I was taking photographs of the fence. They went on Google and looked at some of my work and decided I was genuine."

We parked on a road of ungentrified Victorian houses and council flats round the corner from the Olympic park. Dettmers, who is a brisk and skinny 55-year-old, quickly led me to a canal bridge at the end of the road. And there it was on the far bank: a thick band of blue, slightly blinding against the dull sky, the soupy green of the canal and the dusty green of the late-summer Lea Valley. From 20m away, the fence looked impossibly pristine and smooth, as if an architect's computer graphic had been laid across a landscape photograph. We crossed the canal and started following the fence south.

Up close, it was formidable. Panels of thick plywood had been screwed to heavy posts; the posts were anchored deep in concrete, and joined to each other - it took a while to find a gap in the fence wide enough to glimpse this - by further large horizontal lengths of timber. Along the bottom of the fence, every time the ground dipped, the possibility of squeezing under was blocked by skirting boards and more concrete. The top of the fence was so far above our heads, beyond it we could see only treetops. From the other side, periodically, came near-deafening mechanical hums and groans and clankings. There were no windows in the fence, as there usually are on large London building sites, for passers-by to see what is going on. Along the towpath, which used to be popular with walkers and cyclists, we met almost nobody and there was no graffiti. It was as if the fence had scared everyone away.

We reached a road bridge that until this summer connected two local industrial estates. The fence cut the bridge in half: on the west side of the canal, there was the usual grimy bustle of Hackney's remaining factories, all wheezing forklifts and tight Victorian yards; on the 2012 side, silence. I looked through an unusually large gap in the fence. There was a street of intact and handsome old industrial buildings, a billboard advertising the new Lexus, and roads and pavements eerily populated only by traffic cones, like a scene from a post-apocalyptic film. Dettmers warned me to enjoy the view while I could. "I've come to the Olympic site sometimes," she said, "and buildings I've been familiar with for 10 years have completely vanished."

Trying to sound cheerier, she pointed out one of the fence's rare stretches of lingering graffiti: a few yards of hasty black marker pen momentarily dulling the blue on a secluded section of the bridge. Of the slashes and scrawls, two were easily decipherable. One showed the rings of the traditional Olympic logo hanging from a gallows. The other showed pounds and euros and dollars pouring into a black hole marked "OLYMPIC DEATH PIT".

A certain nostalgia-tinged affection for the lower Lea Valley, with its fading industry and canals and ancient marshes, had been building up like one of the area's winter fogs even before it was announced in 2005 that the Olympics would change the valley for ever. Well-known explorers of London such as the writer Iain Sinclair and the musician Jah Wobble have been writing about this part of the city for at least a decade, as an atmospheric zone of entropy and escape close to the frantic centre of the city. Since the 2012 announcement the cult of the old Lea has burgeoned. Last year the pop group and celebrators of the capital St Etienne released an acclaimed documentary about the area, What Have You Done Today, Mervyn Day? Laments for the valley's disappearing landmarks began appearing in newspapers: "The Hackney fridge mountain is already gone," reported the Independent on Sunday last January. "Can the cooking-fat recycling plants and the kebab-meat factories on Pudding Mill Lane ... be far behind?"

In one sense, there is something too romantic about this view of the area. A bit of industrial rawness and picturesque dereliction can make a stimulating urban ramble - I have nosed around the valley myself for a decade and a half - but you do wonder how many of its enthusiasts actually live in the area, with its fringe of isolated council estates and, until the Olympics, probably limited economic prospects. I never have.

Dettmers, however, makes a more credible defender of the old status quo. Before the Olympics came, she spent years renting cheap studios in the area. On Monday we found a vantage point overlooking the fence and she pointed out one of them. It was a solid-looking brick building with big windows and long views. It was right in the middle of the Olympic site, and what we could see was that everything inside it had been removed. Dettmers started speaking more slowly than usual. "You could cycle here in the evening in the summer," she said, "when the heat was rising from the ground, and it mixed with the smell of spices, with the smell of cinnamon from the food businesses that were round here. You had some Nigerian nightclubs that didn't open until 2am, people training circus artists, what they called 'taxi hospitals', illegal raves, quite a bit of illegal stuff. It was always a bit dangerous, but it was a kaleidoscope of London life."

We turned back to the fence. Here, in the southern section of the Olympic park near the main stadium site, it doggedly dipped and climbed, always trying to shut off the view, following the contours of the land like a cheap builder's version of the Great Wall of China. Then, in a hollow, the blue stopped. For perhaps 100m, the fence was shinier and multicoloured. Mounted on it were a series of messages from the Olympic authorities: the logos of the 2012 games' "World Wide Partners" - among them Coca-Cola, Samsung and McDonald's; computer images of the completed Olympic Park, all water features, spotless curves and diagonals; statistics about the Olympic facilities - "9,715 cubic metres of water in the aquatics centre"; and, perhaps most pertinently, the current slogans of the Olympic Delivery Authority - "Everyone's 2012" and "Demolish. Dig. Design."

Between now and 2012, an ODA spokesman told me the next day, "key parts of the fence will be branded" with these collaged sections. But the fence is branded already. Its ostentatious blue is one of the colours of the bold, shape-shifting, nu-rave referencing, and so far divisive 2012 logo. Day and night, this giant advertisement, like the Olympic site as a whole, is patrolled by private security men. Towards the end of Monday morning, on a public footpath surrounded on three sides by walls of blue, Dettmers and I encountered a trio of them.

"This is a private area," said the first, gesturing vaguely in all directions. But then his body language relaxed and he went back to smoking his roll-up. Dettmers asked him about himself. "I used to work in a shop," he said. "But I got sick of that." Behind him another guard had his head in a paperback, and did not even look up at us. The third guard simply stared into space. Later, another security man told me: "People do try to break in to nick stuff. Sometimes we have to get the police. But the people always get away before the police come."

At lunchtime, Dettmers had to go off and I continued round the fence alone for hours. I passed places where rough sleepers had made shelters against the blue panels; places where old walls and buildings had been incorporated into the barrier; places where small sections of the fence had been carefully cut out to avoid damaging trees; and places, under bridges and in thickets, where you could imagine trying to climb over. Occasionally, there was a view into the Olympic site, where diggers sat on mounds of rubble, swivelling like giant, triumphant insects.

The blue grew on me a little. It made the fence more than the usual kind of shabby builder's hoarding. But on the Hackney Wick estate that faced the longest stretch, people were less enthusiastic. "None of us like the blue," said an elderly woman whose front windows were full of it. "The ducks don't come to the canal any more," said a younger neighbour. "And there are more mice on this side now. I think they've come across." One man told me: "I don't mind the blue so much, but when the wind blows, the dust from the building site comes in. You're forever sweeping the place out." He ran a finger along a moulding on his front door: "It's not too bad today. But all those millions for the Olympics ... Three weeks, and it's all finished."

On the Stratford side of the Olympic park, I talked to a woman who had been living on a local traveller site for 36 years. The Olympic village is going to be built on top of it. "My mother and my father died on here," she said. "I thought I was going to go in a box from here. Now we're supposed to be moving out on Friday." Her family compound, like the half dozen others along the quiet dead-end road, was a homely chaos of caravans and other vehicles - "Fast As Fuck" said a big sticker on the rear windscreen of her jeep - but there was more melancholy than defiance in her view of the Olympics. After a long legal battle, she and her neighbours had agreed to move to a new purpose-built traveller site closer to the middle of Stratford. "Living here we could do what we wanted, as long as we didn't smash the place up," she said, "but we've got to live by their rules now."

The recent history of London, like that of Britain's other smartened-up cities, is full of such uprootings. The cleansing of the Lea Valley follows that of Covent Garden in the 70s and 80s, Docklands in the 80s and 90s, King's Cross between the 90s and now. Steadily, the ragged holes in the city's fabric are being stitched up. It is hard to deny that some benefits - economic, architectural, for consumers - have come with this. But Dettmers, who arrived in London from Germany in 1981, is increasingly alarmed: "Cities need to have holes in them," she says. "Places where they can breathe - valves where the unexpected can be let out."

Late on Monday afternoon, I went back to have another look at her old studio. There were men inside it wearing yellow vests. Through one of the big windows I could see a pneumatic drill leaning against a wall. One of the men picked it up and began digging up the floor.

Not everyone around the Olympic site is sad to see such things happening. Near a particularly impregnable section of the perimeter, a double layer of blue jutting right out over the canal, I met Remis Skucas, a carpenter from Lithuania. He was standing with his big arms folded, beside a gap that had suddenly appeared in the barrier. "I just open and close the fence," he said, nodding at an engineer at work behind him.

I asked Skucas what he thought of what was happening to the Lea Valley. He blew out his cheeks: "I don't know when they're going to start the action. The environmental people mess everything up. They find some pigeon nest, and all work stops."

The blue fence is also a little less all-conquering than it first appears. Already, in places, the paint is flaking off, and without the paint the plywood panels will rot when it rains. On Tuesday, I returned to a stretch I had noticed the day before, a series of oddly unpainted panels next to a busy dual carriageway. It was a brilliant, cloudless morning, but the blue sections of the fence were still garish against the sky. Before I reached the unpainted stretch, I came across a huge and unexpected whirl of graffiti. Its silver spray-paint was still wet to the touch. A man in a yellow vest sat in a car next to it, reading the Sun. I knocked on his window. "We get graffiti on the fence all the time," the man said. "They do it every couple of days. I've got a lad who cycles round, checking the fence every morning. I've got another lad who'll be round in a minute to paint over this lot."

A van pulled up. A middle-aged man with deep blue eyes got out, and unhurriedly put on clean overalls. Then he produced a large tin of paint - the label said "Dulux Trade High Gloss Water Resistant", but not the name of the colour within - and poured it into a tray. I asked him where the blue paint came from. "There are stores full of it," he said. "It's kept on-site, in the main cold store." His roller and brush were already thickly clotted with blue. Did he ever get sick of it? "No, I enjoy the work. I worked on the Channel Tunnel. This is similar. There's good money ..." He turned his blue gaze to the fence: "The best of everything has gone into this, the best of materials." And then, with a few easy strokes of his roller, the graffiti disappeared into the blue of the fence like a thin pencil mark under an eraser.